This invention relates to a line of sight guidance system, and in particular, to a guidance system for a beam rider projectile. While the invention is discussed in particular detail with respect to its missile control application, those skilled in the art will recognize the wider applicability of the inventive concepts disclosed hereinafter. In particular, the invention relates to a method for providing an encoded beam pattern in which the apparent central axis of the beam along a target aim point is shifted to a second axis so that a receiver in the beam is provided with a lead angle component. The lead angle component preferably is based on target tracking rate, wherein the second axis is made to lead the target aim point.
This invention deals with improvements in guidance systems, and in particular, to a guidance system similar to that disclosed in the U.S. Pat. to Esker et al, U.S. Pat. No. 4,014,482, issued Mar. 29, 1977, with which the invention disclosed hereinafter finds application. Details of the guidance system and a missile employed with that system not specifically set forth herein are intended to be incorporated by reference to the Esker et al patent and to the U.S. Patent to Tucker, U.S. Pat. No. 3,868,883, issued Mar. 4, 1975, incorporated by reference in Esker et al, U.S. Pat. No. 4,014,482.
The guidance system disclosed in Esker et al, U.S. Pat. No. 4,014,482, includes a beam projector at a launch site, and a beam receiver and signal decoder carried by the missile. The beam projector employes a laser diode source, laser pulse driver circuits, beam encoder, optic means for projecting the encoded beam, and electronic circuits for controlling the optic means operation. The beam encoder utilizes a reticle having a plurality of spokes formed in it, an opto-interupter for sensing reticle center rotation rate, and drive motor control electronics. The reticle has a center mounted for rotation orbitally about the generated beam so that at least a portion of the reticle intersects the beam in all positions of the reticle. The laser diode source is pulsed at two different rates, those rates being coordinated with the angular position of the reticle center. The laser beam is encoded by rotating the center of the reticle about an axis of the optical system in conjunction with the variation of the pulse repetition rate of the laser source to produce a spatial modulation of the radiated beam. Since the speed of rotation of the reticle center remains constant in U.S. Pat. No. 4,014,482, the missile attempts to align itself with the projected beam axis, where the spatial frequency modulation is a minimum.
While the invention described in Esker et al works well for a stationary beam, the accuracy of the system has been found less than optimized when the beam platform or beam itself is moving and in certain other operating conditions. As indicated above, the guidance system of this invention is designed for use with a number of projectile types. Some launching and projectile types offer more disturbance or recoil to the operator of the projectile system during launch than others. This invention permits the operator greater accuracy by maintaining the beam axis stable during the disturbance, permitting the missile to fly the shifted beam axis rather than the operator's instaneous line of sight aim. Improvement in system accuracy is significant at relatively short operating ranges. Likewise, use of the system described in Esker et al with targets moving at relatively high rates of speed can result in target misses because the actual projectile position often lags behind the moving target line of sight and the collimated center of the projected beam.
The operational performance of the guidance system disclosed in Esker et al can be improved appreciably, particularly with respect to moving targets by providing lead angle information to the missile receiver. Lead angle information is obtained by varying the rate of orbital rotation of the reticle about the optical system axis. That is to say, during each revolution of the reticle center about the optical system axis, the rotational rate of the reticle center is increased and decreased cyclicly to provide lead angle information to a projectile in the beam. The basic technique consists of frequency modulating the rotational rate of the reticle. The frequency modulation amplitude is made to equal the magnitude of the desired angular change in the projected spatially coded axis, and the frequency modulation phase is made to equal the direction in which the spatially coded axis shift is desired. The effect that this beam information has on the missile borne receiver is such that the receiver interprets the image of the reticle pattern as if the receiver were displaced from its unmodulated position in a direction from beam center as indicated by the modulation phase. Since the missile control devices operate to direct the missile toward axis center, or minimum frequency modulation, the missile follows the coded axis shift.
In use, the invention gives stabilization to the coded axis when the beam and the beam projector platform are unstabilized, furnishes spatially coded axis lead angle with respect to the beam center to compensate a missile borne guidance control loop containing a position error when in a moving beam, and supplies a manual or an electronic bore sight alignment between the coded beam axis and a gunner's sight when small angular displacement errors exist.
One of the objects of this invention is to provide improved means for controlling the flight of a projectile.
Another object of this invention is to provide a line of sight guidance system with a lead angle component.
Another object of this invention is to provide a guidance system having improved accuracy for guiding a projectile towards the target.
Another object of this invention is to provide a line of sight guidance system which is relatively inexpensive, light weight, portable and which requires little or no special skill or training in its operation.
Another object of this invention is to provide a means for adjusting the orbital speed of rotation of the reticle center about an optical axis along which a beam is projected based on the rate of change of beam projector motion.
Another object of this invention is to provide a guidance system for a beam rider projectile compatible with a wide range of projectile types.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.